In accordance with improvement in functions and throughput of recent electronic devices, there have been provided a composite substrate (hereinafter called a printed board unit) in which a number of printed boards have different functions and are one another coupled by flexible wiring boards with the intention of avoiding the generation of interference (noise) caused by signal patterns having different functions.
Since demands for electronic devices highly integrated and compact in size increase the number of elements to be mounted to a specific board region, a single printed board is incapable of accommodating all the elements. As one of the solutions, there are provided many printed board units each in which a number of printed board are formed into a stack and are one another coupled via cables and connectors.
Some techniques have conventionally arranged a number of printed boards to keep predetermined space via fixing parts (spacers) in such a printed board unit.
For example, as shown in FIGS. 24A and 24B, conventional printed board unit 100 includes printed boards 101 and 103 fixed to each other such that printed board 103 overlaps printed board 101 via spacer 102. FIG. 24A is the top view of printed board unit 100, and FIG. 24B is the front view of printed board unit 100.
Spacer 102 is coupled to printed boards 101 and 103 by screws or sets of a bolt and a nut.
Signal patterns formed on printed boards 101 and 103 are connected to each other by flexible wiring board (FPC: Flexible Printed Circuit board) 104 to let printed boards 101 and 103 cooperate. For example, printed board 101 and printed board 103 function as a common circuit and a high-speed signal unit, respectively. (For example, Japanese Patent Application Laid-Open No. 2003-110210, Japanese Patent Application Laid-Open No. 2003-283072, and Japanese Patent Application Laid-Open No. HEI 8-330699)
Conventionally, spacer 102 has been designed for each printed board unit 100. In other words, the height and other outlines of spacer 102 is determined according to elements to be mounted on printed board 101 and printed board 103 and a location of installation of printed board unit 100 when printed board unit 100 is designed.
For this reason, if a variation or addition of elements to be mounted on printed board 101 or 103 requires modification of spacer 102, the height of spacer 102 is re-determined and another spacer is newly produced, giving inconvenience and increasing the production cost for another spacer.
In production of a number of different kinds of printed board units 100, spacers 102 have to be designed one for each kind of printed board unit 100, requiring both workload and cost.